lib/isc/inet_ntop.c

	inet_ntop.c revision bd911976d51f102751848568ccf56592fd5f6d77
/*
 * Copyright (C) 1996-2001, 2004, 2005, 2007, 2009, 2016, 2017  Internet Systems Consortium, Inc. ("ISC")
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */

/*! \file */

#if defined(LIBC_SCCS) && !defined(lint)
static char rcsid[] =
    "$Id: inet_ntop.c,v 1.21 2009/07/17 23:47:41 tbox Exp $";
#endif /* LIBC_SCCS and not lint */

#include <config.h>

#include <errno.h>
#include <stdio.h>
#include <string.h>

#include <isc/net.h>
#include <isc/print.h>
#include <isc/string.h>

#define NS_INT16SZ   2
#define NS_IN6ADDRSZ    16

/*
 * WARNING: Don't even consider trying to compile this on a system where
 * sizeof(int) < 4.  sizeof(int) > 4 is fine; all the world's not a VAX.
 */

static const char *inet_ntop4(const unsigned char *src, char *dst,
                  size_t size);

#ifdef AF_INET6
static const char *inet_ntop6(const unsigned char *src, char *dst,
                  size_t size);
#endif

/*! char *
 * isc_net_ntop(af, src, dst, size)
 *  convert a network format address to presentation format.
 * \return
 *  pointer to presentation format address (`dst'), or NULL (see errno).
 * \author
 *  Paul Vixie, 1996.
 */
const char *
isc_net_ntop(int af, const void *src, char *dst, size_t size)
{
    switch (af) {
    case AF_INET:
        return (inet_ntop4(src, dst, size));
#ifdef AF_INET6
    case AF_INET6:
        return (inet_ntop6(src, dst, size));
#endif
    default:
        errno = EAFNOSUPPORT;
        return (NULL);
    }
    /* NOTREACHED */
}

/*! const char *
 * inet_ntop4(src, dst, size)
 *  format an IPv4 address
 * \return
 *  `dst' (as a const)
 * \note
 *  (1) uses no statics
 * \note
 *  (2) takes a unsigned char* not an in_addr as input
 * \author
 *  Paul Vixie, 1996.
 */
static const char *
inet_ntop4(const unsigned char *src, char *dst, size_t size)
{
    static const char *fmt = "%u.%u.%u.%u";
    char tmp[sizeof("255.255.255.255")];

    if ((size_t)sprintf(tmp, fmt, src[0], src[1], src[2], src[3]) >= size)
    {
        errno = ENOSPC;
        return (NULL);
    }
    strlcpy(dst, tmp, size);

    return (dst);
}

/*! const char *
 * isc_inet_ntop6(src, dst, size)
 *  convert IPv6 binary address into presentation (printable) format
 * \author
 *  Paul Vixie, 1996.
 */
#ifdef AF_INET6
static const char *
inet_ntop6(const unsigned char *src, char *dst, size_t size)
{
    /*
     * Note that int32_t and int16_t need only be "at least" large enough
     * to contain a value of the specified size.  On some systems, like
     * Crays, there is no such thing as an integer variable with 16 bits.
     * Keep this in mind if you think this function should have been coded
     * to use pointer overlays.  All the world's not a VAX.
     */
    char tmp[sizeof("ffff:ffff:ffff:ffff:ffff:ffff:255.255.255.255")], *tp;
    struct { int base, len; } best, cur;
    unsigned int words[NS_IN6ADDRSZ / NS_INT16SZ];
    int i;

    /*
     * Preprocess:
     *  Copy the input (bytewise) array into a wordwise array.
     *  Find the longest run of 0x00's in src[] for :: shorthanding.
     */
    memset(words, '\0', sizeof(words));
    for (i = 0; i < NS_IN6ADDRSZ; i++)
        words[i / 2] |= (src[i] << ((1 - (i % 2)) << 3));
    best.base = -1;
    cur.base = -1;
    for (i = 0; i < (NS_IN6ADDRSZ / NS_INT16SZ); i++) {
        if (words[i] == 0) {
            if (cur.base == -1)
                cur.base = i, cur.len = 1;
            else
                cur.len++;
        } else {
            if (cur.base != -1) {
                if (best.base == -1 || cur.len > best.len)
                    best = cur;
                cur.base = -1;
            }
        }
    }
    if (cur.base != -1) {
        if (best.base == -1 || cur.len > best.len)
            best = cur;
    }
    if (best.base != -1 && best.len < 2)
        best.base = -1;

    /*
     * Format the result.
     */
    tp = tmp;
    for (i = 0; i < (NS_IN6ADDRSZ / NS_INT16SZ); i++) {
        /* Are we inside the best run of 0x00's? */
        if (best.base != -1 && i >= best.base &&
            i < (best.base + best.len)) {
            if (i == best.base)
                *tp++ = ':';
            continue;
        }
        /* Are we following an initial run of 0x00s or any real hex? */
        if (i != 0)
            *tp++ = ':';
        /* Is this address an encapsulated IPv4? */
        if (i == 6 && best.base == 0 && (best.len == 6 ||
            (best.len == 7 && words[7] != 0x0001) ||
            (best.len == 5 && words[5] == 0xffff))) {
            if (!inet_ntop4(src+12, tp,
                    sizeof(tmp) - (tp - tmp)))
                return (NULL);
            tp += strlen(tp);
            break;
        }
        tp += sprintf(tp, "%x", words[i]);
    }
    /* Was it a trailing run of 0x00's? */
    if (best.base != -1 && (best.base + best.len) ==
        (NS_IN6ADDRSZ / NS_INT16SZ))
        *tp++ = ':';
    *tp++ = '\0';

    /*
     * Check for overflow, copy, and we're done.
     */
    if ((size_t)(tp - tmp) > size) {
        errno = ENOSPC;
        return (NULL);
    }
    strlcpy(dst, tmp, size);
    return (dst);
}
#endif /* AF_INET6 */